1 Atomic structure & periodicity

Question 1

Define Isotope

Answer 1

Atoms of the same element with the same number of protons but a different number of neutrons.

Question 2

Define 1st Ionisation energy

Answer 2

The energy required to remove 1 mole of electrons from 1 mole of gaseous atoms to form 1 mole of gaseous ions with a 1+ charge.

Question 2

Define Mass Number

Answer 2

The total number of protons and neutrons in the nucleus.

Question 3

Define Nuclear Charge

Answer 3

Total charge of all the protons in the nucleus.

Question 4

Define Sub-shells

Answer 4

Electrons shells divided up into sub-shells (S,P,D,F) which have slightly different energy levels.

Question 5

Define Orbitals

Answer 5

Sub-shells contain different numbers of orbitals which can each hold up to two electrons.

Question 6

Define Relative Atomic Mass

Answer 6

The weighted average mean mass of all isotopes of an element relative to 1/12th the mass of an atom of C12.

Question 7

How does atomic radius change across period 3?
How does First Ionisation energy change across period 3?

Answer 7

Radius: Decreases
Ionisation: Increases

Explanation:
Increased nuclear charge
Similar Shielding
Stronger attraction between valence electrons and nucleus.

Question 8

Exceptions to 1st Ionisation energies in Period 3?

Answer 8

Sulphur:
1st P orbital to have 2 electrons.
Mutual repulsion
Less energy requires.

Aluminium:
Electrons removed from p orbital
Higher energy level
Less energy required.

Question 9

How do successive ionisation energies change?

Answer 9

Increase:
each electron is harder to be removed than the previous.
Greater attraction to an already positive ion.

Question 10

Rule for electron sub-shell stability? Elements that use this?

Answer 10

Half full or full d sub shells are more stable.
Cr and Cu use a 4s electron to get the half full/full d sub-shell.

Question 11

What are the four stages of TOF?

Answer 11

Ionisation
Acceleration
Drift
Detection

Question 12

What are the two types of ionisation?

Answer 12

Electrospray (adds proton +1 to mass)
Electron impact (removes electron)

Question 13

What is acceleration TOF?

Answer 13

Positive ions are accelerated by an electric field and given the same KE.

Question 14

What is drift TOF?

Answer 14

ions drift through a tube with no electric field, lighter ions move faster.

Question 15

What is detection TOF?

Answer 15

Ions accept an electron at the positive plate, current proportional to abundance.

Question 16

What is Electrospray ionisation TOF (Method)?

Answer 16

Sample dissolved in volatile solvent (Water/methanol)
Injected through fine hypodermic needle to fine mist.
Tip attached to + terminal of a high-voltage supply.
Ionised by gaining a proton as they leave the needle.

Question 17

How to calculate Ar of a sample from abundance?

Answer 17

sum of mass x abundance/ total abundance

Question 18

What does TOF calculate?

Answer 18

Mass and abundance

Question 19

What rare occurrence can happen in TOF?

Answer 19

Ions produced with a 2+ charge will half the mass of the isotope on a Mass Spec.

Question 20

What is the difference in properties of isotopes of the same element?

Answer 20

No difference as they have the same electron configuration.

Question 21

Define atomic number?

Answer 21

Number of protons.

Question 22

What are on the axes of a Mass Spec?

Answer 22

Relative Abundance (Y)
Mass/Charge (X)

Question 23

What is Electron impact TOF (Method)?

Answer 23

High Speed Electrons fired from a hot wire filament knocks out an electron from orbit.

Question 24

Explain the existence of isotopes.

Answer 24

Isotopes exist due to instability caused in an atom. (Radioactive decay).

Question 25

How does melting point change across period 3?

Answer 25

Metallic elements MP increases (Na-Al):
More delocalisation of electrons per atom, Higher charge density, more energy required to overcome electrostatic forces.

Silicon MP is very high:
Giant covalent, lots of energy required to break strong cov bonds.

P,S,Cl,Ar MP are low:
Simple covalent, little energy required…

Of P,S,Cl,Ar:
S8 P4 Cl2 Ar,
IMF greater van der waals in larger molecules, requires more energy to overcome.

Question 26

How to calculate isotope mass from abundance?

Answer 26

(isotope 1 x abundance) + (isotope 2 x abundance) / total abundance

Question 27

Why is TOF in a vacuum

Answer 27

The whole TOF:MS is kept under this condition to prevent interference of foreign particles